Flow fields of graupel falling in air

The flow fields of conical graupel of diameters 0.5–5 mm falling in air of 800 hPa and − 20 °C are studied by solving the relevant Navier–Stokes equations numerically using the ANSYS Fluent as the solver. The range of Reynolds numbers investigated in this study is from 20.12 to 1084.16. A steady state solution is obtained first and is perturbed by adding an instantaneous velocity perturbation. The flow solutions for the cases of 0.5, 1 and 2 mm graupel return to steady state after a brief transient period. The solutions for 3, 4 and 5 mm become unsteady with eddy shedding. The eddy shedding appears to become more turbulent for larger graupel. The characters of the flow fields are illustrated using the velocity, pressure distribution, and streamtrace fields. The computed drag coefficients are compared with that for spheres and disks of the same Reynolds number range and are found to be closer to spheres rather than disks.

► We obtained numerical solutions of the flow fields around falling conical graupel.
► Flow fields around falling graupel with diameter greater than 3 mm are unsteady.
► Maximum and minimum deviation pressures vary quasi-linearly with Reynolds number.
► The number and frequency of small transient eddies increases with Reynolds number.